Document FR553667 describes a first damper comprising a piston furnished with a head traversed by a through rod, this through rod having an upper rod and a lower rod on either side of the piston head.
The piston head then slides in a compression chamber of the damper, the lower and upper rods of the piston being respectively in the lower portion and the upper portion of the compression chamber.
In addition, the compression chamber comprises a plurality of radial bores, placed longitudinally over its periphery, these radial bores opening onto a channel connecting the upper portion of the compression chamber to its lower portion. Note that each bore is obstructed by a valve.
When the damper is stressed in compression, the piston makes a translation movement and expels the fluid contained in the upper portion of the compression chamber via the radial bores.
This expulsion causes a throttling of the fluid which thereby generates a damping.
Note that the piston head masks the radial bores one after the other, as the piston progresses in the compression chamber. Consequently the section of leakage of the fluid diminishes with the progression of the piston which makes it possible to progressively increase the damping generated by the damper.
This first damper therefore fulfils a damping function well. Nevertheless, if the piston moves slowly, it is understood that the damping will be virtually non-existent. Also, being inversely proportional to the dimension of the bores, a large-sized bore that is easy to produce induces a weak damping action.
Document FR2601097 has a second damper provided with a piston sliding in a sealed manner inside a compression chamber.
The piston being of cylindrical shape, the lower base of the piston entering the compression chamber is furnished with longitudinal orifices.
These orifices make it possible to place the compression chamber of the damper in communication with a hydraulic chamber inserted in the piston rod.
During an axial movement of the piston, caused by the compression of the damper, the fluid of the compression chamber is throttled by the longitudinal orifices in order to enter the hydraulic chamber, which is the source of the damping achieved by the damper.
In addition, the piston rod grips elastic means in contact with the hydraulic chamber.
Since the hydraulic chamber fills with the fluid originating from the compression chamber via the longitudinal orifices, the volume of this hydraulic chamber tends to increase which causes the elastic means to contract.
Consequently, when the rotorcraft lands, the piston moves rapidly which induces a throttling of the fluid of the compression chamber.
On the other hand, in a static situation, when the rotorcraft is on the ground, the piston will not move rapidly. The damping will then be generated by the contraction of the elastic means.
This second damper therefore makes it possible to fulfil a damping function, both according to the speed of movement of the piston but also according to its movement, because respectively of the longitudinal openings and the elastic means.
However, unlike the first damper, it is noted that this second damper does not provide any variable-section radial bores, the longitudinal orifices not being provided in order to be obstructed notably. The throttling of the fluid, and the resultant damping, can therefore not be modulated and adapted according to the situation encountered with the aid of such bores. However, the second damper is fitted with a throttle needle for filling a similar function.
It is noted that the technical features of the first damper would not be able to be used in the context of the second damper, the throttling orifices being on the one hand longitudinal and not radial, and, on the other hand, placed on the piston itself, this piston therefore not being able to mask its own orifices.